In recent years, canned motors having a structure including a motor drive chamber and a rotor chamber separated from each other by a diaphragm have been widely used. Such motor is used for a pump for transporting pure water in a semiconductor manufacturing line used in an environment that avoids dust, and a pump for transporting a biological solution, for example. Pumps for transporting a biological solution include a centrifugal blood pump apparatus using a direct drive motor for directly transmitting torque to an impeller in a blood chamber. This centrifugal blood pump apparatus can eliminate physical contact between the blood chamber and the outside to prevent invasion of bacteria and the like into blood, and is thus used as an artificial heart. Since an artificial heart is driven by electric power from a battery, enhancement of motor efficiency is critical.
A centrifugal blood pump in Japanese Patent Laying-Open No. 2004-209240 (PTL 1) includes a housing having first to third chambers partitioned from one another by first and second diaphragms, an impeller rotatably provided in the second chamber (blood chamber), a magnetic material provided in one surface of the impeller, an electromagnet provided in the first chamber to face the one surface of the impeller, a permanent magnet provided in the other surface of the impeller, a rotor and a motor provided in the third chamber, and a permanent magnet provided in the rotor to face the other surface of the impeller. Grooves for hydrodynamic bearing are formed in a surface of the second diaphragm facing the other surface of the impeller. Due to an attractive force acting on the one surface of the impeller from the electromagnet, an attractive force acting on the other surface of the impeller from the permanent magnet in the rotor, and a hydrodynamic bearing effect of the grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the second chamber, and rotates without contacting.
A centrifugal blood pump in Japanese Patent Laying-Open No. 2006-167173 (PTL 2) includes a housing having first to third chambers partitioned from one another by first and second diaphragms, an impeller rotatably provided in the second chamber (blood chamber), a magnetic material provided in one surface of the impeller, a first permanent magnet provided in the first chamber to face the one surface of the impeller, a second permanent magnet provided in the other surface of the impeller, a rotor and a motor provided in the third chamber, and a third permanent magnet provided in the rotor to face the other surface of the impeller. First grooves for hydrodynamic bearing are formed in a surface of the first diaphragm facing the one surface of the impeller, and second grooves for hydrodynamic bearing are formed in a surface of the second diaphragm facing the other surface of the impeller. Due to an attractive force acting on the one surface of the impeller from the first permanent magnet, an attractive force acting on the other surface of the impeller from the third permanent magnet in the rotor, and a hydrodynamic bearing effect of the first and second grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the second chamber, and rotates without contacting.
A turbo-type pump in FIGS. 8 and 9 of Japanese Patent Laying-Open No. 4-91396 (PTL 3) includes a housing, an impeller rotatably provided in the housing, a first permanent magnet provided in one surface of the impeller, a rotor provided outside of the housing, a second permanent magnet provided in the rotor to face the one surface of the impeller, a third permanent magnet provided in the other surface of the impeller, and a magnetic material provided in the housing to face the other surface of the impeller. First grooves for hydrodynamic bearing are formed in the one surface of the impeller, and second grooves for hydrodynamic bearing are formed in the other surface of the impeller. Due to an attractive force acting on the one surface of the impeller from the second permanent magnet in the rotor, an attractive force acting on the other surface of the impeller from the magnetic material in the housing, and a hydrodynamic bearing effect of the first and second grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the housing, and rotates without contacting.
A clean pump in Japanese Utility Model Laying-Open No. 6-53790 (PTL 4) includes a casing, an impeller rotatably provided in the casing, a first permanent magnet provided in one surface of the impeller, a rotor provided outside of the casing, a second permanent magnet provided in the rotor to face the one surface of the impeller, a magnetic material provided in the other surface of the impeller, and an electromagnet provided outside of the housing to face the other surface of the impeller. Grooves for hydrodynamic bearing are formed in the one surface of the impeller. The electromagnet is operated when a rotation speed of the impeller is lower than a predetermined rotation speed, and power supply to the electromagnet is stopped when the rotation speed of the impeller becomes higher than the predetermined rotation speed. Due to an attractive force acting on the one surface of the impeller from the second permanent magnet in the rotor, and a hydrodynamic bearing effect of the grooves for hydrodynamic bearing, the impeller moves away from an inner surface of the housing, and rotates without contacting.